Automatic telephone system



.Sept. 8, 1925.

C. E. LOMAX AUTOMATIC TELEPHONE SYSTEM ed March 25, 1921 2 Shun-Shoot 1 Harm-m5 EJLmnax Sept. 8, 1925.

C. E. LOMAX AUTOMATIC TELEPHONE SYSTEM 2 Shuts-Shoot 2 nun. "nun" ill Filed March 25 1921 -I:u r5n UP-- Elarenma E.LUH'LEX Patented Sept. 8, 1925.

UNITED STATES PATENT OFFICE.

CLARENCE E. LOMAX, OF CHICAGO, ILLINOIS, ASBIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION 01 ILLINOIS.

Applteation flled 1mm 25, 1921. Serial no. 455,698.

To all whom it my camera:

Be it known that I, CLARENCE E. LOMAX, a citizen of the United States of .America, and a resident of Chicago, Cook County, and State of Illinois, have invented certam new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

The present invention relates in general to automatic telephone systems; and the object of the invention is to rovide new and improved service and tra c observing arrangements for use in such a system.

More specifically, according to one feature of the invention, an arrangement is provided whereby an operator may observe the service on a complaining subscribers line with a view to ascertaining Whether or not the complaints are well founded, and if so, their precise nature, in order that they may be remedied. Signals are provided to notify the observing operator 0 an incoming or outgoing call on the complaining subscribers line, and meters are also provided as an additional check to register the total number of such calls.

According to a further feature of the invention, meters are provided at certain points in the trunking system where it is suspected that the trunk groups are too small to adequately handle the trafiic, the object being to obtain traffic data from which to revise the trunking facilities, or provide additional facilities if it should prove to be necessary. In this connection circuit arrangements are provided for enabling an observing operator to answer calls,

which fail because the trunking facilities are inadequate.

These features and modifications thereof will be fully explained hereinafter with reference to the accompanying drawings, in which the invention is shown as embodied in a well known type of telephone system.

Referring to therdrawings, in order to properly illustrate and explain the invention it has been considered desirable to show certain apparatus used in a regular automatic telephone connection, and Figs. 1 and 2 show, therefore, by means of the usual circuit diagrams certain apparatus in an automatic telephone system which may be used by a subscriber at substation A for the purpose of establishing a connection with a subscriber at substation A, together with and their functions will be briefly pointed out.

The substation A, Fig. 1, is the wellknown type of automatic substation in common use. The calling device S is of the standard two wire type and is provided for the purpose of enabling the subscriber to control the central ofiice switches. The substation A is exactly like the substation A.

The reference character C denotes an individual line switch of the well known Keith, or plunger type. A group of these hne switches, usually 100 in number, is controlled by the master switch MS.

The reference character D indicates a first selector switch of the well known Strowger vertical and rotary type. As is well known, the bank contacts of a switch of this type are divided into horizontal levels with ten contact sets perlevel, and the drawing shows the last five contact sets in the first three levels.

The second selector E, Fig. 2, is similar to the first selector D. The last five sets of bank contacts in the first three levels are also shown in connection with this switch.

The reference character H indicates a connector switch of the Strowger vertical and rotary type which is one of a plurality of similar connectors having access to a group of subscribers lines, one of which is the line of substation A. In view of the fact that connector circuits are not necessary for an understanding of the invention most of these circuits have been omitted.

The apparatus comprising the service and tratfic observin equipment may now be briefly describe Keys K K and K, together with other similar keys, are located at the observing operators position. Lamps line switches.

tions indicated thereby. The meters M to M", inclusive, and other similar meters, are preferably located on a rack at any convenient point in the exchange.

Before proceeding with the explanation of the operation it will be necessary to explain about the line switch C a little more in detail. This line switch is not permanently associated with the line of substation A as might be inferred, but is a special line switch located on this particular 100 line unit, which so arranged that it may be assigned to any subscribers line in the group. The line switch associated with number 99 may be conveniently used for this purpose, since this number is rarely assigned as a Working line. The switch modified by the addition of two relays, relays 15 and 16, and conductors are extended to the service observing operators position as illustrated in the drawing. The conduc tors 42, 43, and 44 are formed into a flexible cable and are connected to a terminal strip comprising a set of male jacks, such as is usually provided for each of the individual In case it is desired to observe the service on any subscribers line, the line switch normally assigned to such line is removed from the switchboard and the special terminal, just described, is inserted in the female 'ack associated with the line of the complaining subscriber. With this arrangement, the line in question is now given service by way of the special line switch, shown in the drawing, and the. incoming and outgoing calls can be observed by the operator as will be described. It is understood, of course, that each 100 line unit may be equipped with a special line switch, similar tothe line switch C, so that any subscriber in the exchange may be given special attention whenever required.

Having described the apparatus involved, the operation of the system will now be described somewhat more in detail in order that the particular features of the invention may be clearly understood. It will be advisable, however, before considering the service and tratiic observing arrangements to explain briefly the operation of the automatic switches in setting up a connection, and this explanation will now he proceeded with. Assuming that the subscriber at substation A, Fig. 1, whose line is under observation, desires to obtain connection with the subscriber at substation A, Fig. 2, when the receiver is removed at substation A a circuit is completed over the line conductors l1 and 12 for the line relay 14 of the special line switch C. Upon energizing, relay 14 closes a circuit for the pull in winding 18 of the line switch which at once operates to attract both the cut-off armature 23 and the plunger arm 24, the latter being shown only in part. By the attraction of the cutoff armature 23, the line conductors 11 and 12 are disconnected from the line relay l4 and from ground, respectively; while the operation of the plunger arm forces the bank springs 30, 31, 32, and 33 into engagement with contacts 34, 35, 36, and 37, respe tively. By the engagement of bank springs lay 54 is energized over the calling line and closes a circuit for the slow acting release relay Upon energizing in turn, relav 55 prepares a circuit for the vertical magnet 58 at its lower armature, and at its upper armature connects ground to the release trunk conductor 51, thereby completing a holding circuit which extends by way of the said conductor 51, contact'35, bank spring 31, and the holding winding 17 of the line switch C to battery. This holding circuit is completed before the slow acting line relay 14 has time to deenergize and by the energization of the holding winding 17 serves to maintain the cut-oil armature 23 and. the plunger arm 24 in operated position. A branch of this holding circuit may be traced through the winding of relay 16, by way of the resting contact of armature 45 and the said armature to battery. Relay 16 is accordingly energized and at its left hand armature short circuits the winding of relay 15. By this operation aground potential is placed upon the private normal conductor 28 in order to render the line of substation A busy to incoming calls. Relay 16 also grounds the conductor 26 extending to the service observing operators position,

but the purpose and function of this operation will be explained later on.

Another result brought about as an incident of the operation of the line switch C is the operation of the master switch MS. When the bank spring 32 is forced into engagement with contact 36, ground is placed upon conductor 38 which extends to a test contact in the master switch bank. As a result a circuit is closed for the master switch starting relay and the said switch is ad vanced, in the usual manner, to move the plungers of all the idle line switches in the group into position before the next idle trunk line.

The calling line having been extended to the first selector D by the operation of the line switch C, the calling subscriber is given an audible signal from the special signalling machine Q, which notifies him that his line is connected with a first selector at the exchange, and that he may now proceed to call the digits in the number of the Wanted subscriber. The calling subscriber will, therefore, operate the dial of his calling device in accordance with the first digit with the result that the line circuit is interrupted a plurality of times. In response tothese interruptions the line relay 54 is momentarily deenergized a like plurality of times, and at each dcenergization transmits a current impulse to the vertical magnet 58 which operates to raise the selector shaft and the wipers 74, 75, and 76 until the latter arrive at the desired level of bank contacts. The slow acting relay 56 is energized in series with the vertical magnet and retains its armature attracted throughout the vertical movement of the switch. At the first upward movement of the switch shaft, the off normal springs 61 and 62 are closed, and since relay 56 is now in operated position a circuit is completed for the stepping relay 57. Upon energizing, relay 57 closes a locking circuit for itself at its upper armature and at its lower armature prepares a circuit for the rotary magnet 59.

An instant after the vertical operation of the switch is completed, the slow acting relay 56 retracts its armature. This closes the circuit of the rotary magnet 59 which accordingly energizes and rotates the switch shaft to bring the wiper into engagement with the first set of contacts in the level opposite which they were raised. At the same time the rotary magnet breaks the locking circuit of the stepping relay 57, which thereupon deenergizes and breaks the circuit of the rotary magnet 59, which accordingly deenergizes also and again closes the interrupter contact which is included in the circuit of the stepping relay. The opera tion now depends upon whether or not the first trunk line in the selected level is busy or idle. If this trunk line is busy, there will be a ground potential upon the test contact engaged by test wiper 75, the stepping relay 57 will again be energized, and the rotary magnet will be operated once more to advance the switch wipers into engagement with the next set of contacts. These operations. in which the stepping relay and the rotary magnet are energized and deenergized alternately, will continue as long as test wiper engages grounded test contacts. As soon as a non-grounded test contact is reached, which we will assume is the test contact 78 associated with the trunk line comprising conductors 80, 81, and 82, the stepping relay 57 will fail to energize again and the rotary movement of the switch will cease. The switching relay 53, which heretofore has been short circuited, is now energized in series with the stepping relay 57, the switching relay being of such high resistance that the stepping relay-remains inoperative. Upon energizing, the switching relay 53 connects the grounded. re-

lease-trunk conductor 51 to the test wiper 75 at armature 69 in order to make the elected trunk line busy at once, and atarmawipers 74. and 76, bank contacts 77 and 79, V trunk conductors 80 and 82, and the upper and. lower armatures of switching relay to the upper and lower" windings of the line 'relay 101 of the second selector E.

When the calling line is extended to the second selector E, as described in the foregoing,-the said line relay is energized and closes a circuit for the slow acting release relay 102. Upon energizingrelav 102 prepares a circuit for the vertical magnet H15 in the usual manner and also connects ground to the release trunk conductor 81. thus establishing a holding circuit which ex tends by way of the said release trunk conductor 81, test contact 78, test wiper 75, and armature 69 and its working contact to the release trunk conductor 51, where it joins the previously described holding circuit extending back to the line switch C. The

switching relay 53 is maintained energized over this circuit throughout the connection.

The calling subscriber may now operate his calling device in accordance with the second digit in the desired number, and as a consequence another series of interruptions is produced in the line circuit which serve to cause a series of deenergizalions of the and at the end of the vertical movement of the switch falls back to initiate the rotary movement. to a connector switch is nowselected the same way as was described in the ('ascof the first selector D, and assuming that the trunk.

An idle trunk line extending line'selected is the one terminating in the connector H, when the wipers are l.n'ou; 'ht

to rest in engagement with lmnkcontacts, 133, 134, and the switching relay 100 is energized and the trunk conductors 80 and 82 are extended through to the windings oi; the double wound line relay of the connector H.

As soon as the line is extended to the connector H, as explained in the foregoing, the line relay 150 is ener ized and closes a circuit for the slow actmg release relay 151. The latter relay is accordingly operated and in addition to preparing a circuit for the vertical n'iagnet ot' the connector (not shown) connects ground to the release trunk conductor 137. By the latter operation a holding circuit is established which extends by way of the said release trunk conductor 137, test contact 134;, test wiper 131, and armature 1-10 and its working contact to the release trunk conductor tt, where it joins the previouslv described holding circuit extending back to the selector 1) and the line switch C. Switching relay 100 in the selector E is thus energized in parallel with the switching relay 53 of the selector 1) throughout the duration of the connection. The remaining operations by which the connection is finally completed are not essen tial to an understanding of the invention and since they are well understood anyway they will be mentioned only briefly. \Vhen the calling subscriber operates his calling device in accordance with the last two digits in the desired number the connector H first raises the wipers 160, 161, and 162 vertically and then rotates them until they come to rest in engagement with the particular set of bank contacts in which the line of substation A is terminated, these bank contacts being indicated in the drawing by reference characters 163, 16-1, and 165. Automatic ringing equipment in the connector is now started in operation to signal the called subscriber. lVhen the called subscriber answers, the ringing operation is automatically Sif()1)] ')t.(.l according .to well knownpractice, and the transn'litter at the called substation is supplied with talking current through the windings of the back bridge relay 153. The transmitter at the calling station is supplied with talking current through the windings of the line relay 150, and since the complete talking circuit has now been established the two subscribers may converse as desired.

The disconnection and release of the automatic switches at the end of the conversation is accomplished in the ordinary manner. When the subscribers arethrough talking they will both replace their receivers, and the replacement of the receiver at substation A results in the deenergization of relays 150 and 151 of the connector H. The latter relay upon deenergizing removes ground from the previously described holding circuit, including release trunk conductors 137, 81, and 51, and as a result the switching relay 100 in the second selector E, switching relay 58 in the first selector D, and the holding winding 17 of the line switch C are deenergized. The line switch C is accordingly restored to normal position in the usual manner, and selectors D and E are'restored to normal by'means of the release magnets 60 and 106. All of the equipment is thus replaced in normal con-' dition ready for use in establishing another connection, and the lines of both calling and called subscribers are. cleared for the reception of incoming calls.

It will be. convenient now to explain the various service and tratiic observing devices, and the first to be considered are the service observing arrangements associated with the special line switch C. \Vhenever the subscriber on the line under observation makes an outgolng call, as was described in the foregoing pages, relay 16 is energized in parallel with the holding winding 17 of the line switch C and places grount't on the conductor 26 extending to the service observing operators position. This causes the lamp L to be lighted and also operates the meter M It'will be seen then that the meter M will register the total number of outgoing calls from this particularline, The lighting of the lamp L notifies the operator that the subscriber is attempting to make a call and if she is not otherwise occupied, the operator will throw the key K in order to connect her head set with the conductors 40 and 41.coming from the special line switch C. Itwill be noted that there is a condenser connected in series with the right hand winding of the induction coil in the operators head set so that the progress of the call will not be interfered with, and the operator can thus observe the call from start to finish, and in ordinary cases can determine the reason for any trouble met with in case the call is not entirely successful.

When the line under observation is called by some other subscriber, the connector switch in use will connect with the called line by way of the normal conductors 27, 28, and 29 and a ground potential will be placed upon the private normal conductor 28 in order to energize the holding winding 17 andoperate the cut-oil armature 2?). It will be observed that relay 15 is included in-the circuit of the holding winding 17 in this case and accordingly is energized at the same time. Although a circuit is closed for relay 16 also, this relay is made slightly slow to energize by means of a copper slug on the core, and before it has time to attract its armature its circuit is opened at armature by relay 15. In operated position relay 15 connects ground to conductor 25, causing the lamp L at the observing operators position to be lighted and also operating the meter M Meter M thus registers the total number of calls incoming to the line under observation. The lighting of the lamp L, of course, attracts the attention of the operator'and she may listen in by means of key K in order to supervise the connect-ion, as was done in the case of an outgoing call.

The traffic observing and metering arrangements associated with the selector switches will now be explained. Considering the first selector switches, the first selector D for example is provided with eleven test contacts in each level, instead of only ten which is the usual number. Thus, referring to the drawing, the test contact 78 is supposed to be the tenth test contact in the second level (the first five sets of contacts are omitted), while the test contact 90 is the eleventh, or additional test contact just referred to. These extra test contacts are provided in order to operate the meters and light the associated lamps in case calls are received while all the trunks are busy, as will be explained presently. The first selector D, and likewise the other first selectors, has a set of rotary oft normal springs comprising contact springs 63 to 67, inclusive, which are operated by the switch shaft upon the eleventh rotary step. With this explanation the operations which take place when a call is received and no idle trunks are available may be considered.

Suppose that the subscriber at substation A attempts to make a call, as was'described before, and that all of the trunk lines in the group selected by the-first selector D are busy. Assuming that the group selected is the group terminating in the second level of the selector I), when the rotary movement of the switch is initiated it will continue, for the test wiper will find all of the test contacts] to 10, inclusive, grounded, and the rotary movement will cease only when the test wiper 75 arrives at the eleventh test contact 90. Since the test wiper finds no ground on this test contact the stepping relay 57 will not be energized again and the rotary movement of the switch will cease. The switching relay 53, however, is not energized as would ordinarily be the case because its circuit is opened on the eleventh step of the switch by the separation of rotary oif normal springs 63 and 64. Since the switching relay is not energized, the test wiper '75 is not grounded and the eleventh test contact is not made busy, thus permitting other selector switches to stop on their eleventh contacts also. When the rotary ofi' normal springs are shifted, in addition to the separation of contact springs 63 and 64, contact spring 65 is brought into engagement with contact spring 67 and the latter is separated from contact spring 66. By this operation, conductor 83 coming from the lower winding of the line relay 54 is disconnected from the signalling machine Q, and is connected instead with the common conductor 87, which extends to the observing operators position and through the winding of relay 84 to ground. Relay 84 is accordingly energized over the calling line and closes a circuit for operating the meter M and for lighting the lamp L When the operator notices the lighting of the lamp L she may talk to the subscriber if she desires by operating key K which connects the right hand winding of her head set induction coil in parallel with the winding of relay 84.

The conductor 87 and the key K and associated equipment are common to an entire group of first'selector switches, and it will be evident now that a number of other calling lines may be connected by means of the rotary o'tt' normal springs in the first selectors in use with the common conductor 87 in case such selectors find all of the trunk lines in the selected groups busy. Since the relay 84 is maintained energized as long as there is any calling line connected with the conductor 87, it will be clear that meter M will not indicate the total number of calls which fail because of inadequate trunking facilities, but will indicate the number of periods of time during which one or more calls are lost because no trunk lines are available.

In order to afford an indication of which of the several groups of trunk lines ac cessible to the first selector switches are over-crowded with traffic, the individual group meters M M, M, and other similar meters are provided, these meters and the associated lamps at the observing operators position being wired to the eleventh test contacts in the switch banks as illustrated. It will be understood, of course, that the eleventh contacts in each level are multipled throughout the entire group of first selectors, so that the meter M for instance is common to all of the first selector switches, but is individual to the group of trunk lines terminating in the second level of said selectors. These meters are operated as follows: Suppose in the preceding case that a number of selector switches in use by calling subscribers have stopped with their test wipers in engagement with the eleventh contact in the second level, the selector D being one of the switches in use, with its test wiper 75 in engagement with the test contact 90. When the calling subscriber who is using the selector D replaces his receiver the line relay 54 will be deenergized and will open the circuit of the slow acting release relay 55. This latter relay is slow acting, however, and before it has time to fall back a circuit is completed momentarily through the slow acting relay 56 and the vertical magnet 58. The switch shaft is now held by the stationary dog and the operation of the vertical magnet 58 is, therefore, ineffective but the slow acting relay 56 upon energizing connects ground to the test wiper 75, and thus closes a circuit for the meter M and the lamp L. An instant later the slow acting relay 55 will fall back and break the circuit through the slow acting relay 56 and will close. the circuit of the release magnet 60 in order to release the selector switch. It will be evident from the foregoing operations, in which the test contact 90 is grounded in order to operate the meter M that the stepping relays such as the relay 57, in all of the other selectors which are standing on the eleventh contact in the same level, will be energized and the rotary magnets in such switches will be operated a few times, but this causes no harm owing to the fact that the rotary ratehets on the switch shafts only have eleven teeth each and the switches are unable to take any additional steps but remain standing on the eleventh contact. N ow as each of the other selectors in use is released, the test contact 90, or rather a multiple thereof, is grounded the same way as was just described in the case of the selector D, and the meter M is thus operated once for each call that is lost because all of the trunk lines in the level with which it is associated are busy.- The lamp L, of course, is flashed momentarily every time the meter is operated and indicates to the operator which group of trunk lines is short of trunking facilities. The utility of this may be pointed out by considering a case where the lamp L remains lighted for an undue length of time, indicating a continuous succession of lost calls. The operator may now observe the flashing of the lamps, such as the lamps L, L or L, as the calling subscribers hang up their receivers and can thus determine which group, or groups, are being overcrowded with trafiic. It may be that the crowded condition is caused by some failure in the switchboard equipment, causing some of the trunk lines to be held busy when they are not actually in use, and the observing operator is thus able to direct the attention of a switchboard attendant to the particular group of trunk lines in trouble.

The arrangement of meters and lamps shown in Fig. 2 in connection with the bank of the second selector E is provided for identically the same purpose as the equipment associated wit-h the bank of the selector D, Fig. 1, but operates in a slightly different manner. This second arrangement is perhaps more desirable than the first because it prevents any rotary movement of the selectors which are waiting on the eleventh contact in case one of them is released, but it requires the addition of a resistance coil in each selector and on that account is ordinarily not used except in new installations. In the exchange system herein illustrated it may be assumed that the first selectors, such as the selector D, are part of the original installation, while the second selectors such as the selector E are installed as an addition at av later date in order to increase the capacity. The manner in which the meters, such as meter M for example, which are associated with the second selectors are operated will now be briefly pointed out. Suppose that the second selector E and a. plurality of other selectors are operated in an attempt to connect with trunk lines in the group which includes the connector H, and let it be assumed further that all of these trunk lines .resistance 143 is connected in series with stepping relay 104. Battery is now supplied through the winding of relay 104 to a circuit which may be traced through resistance 143, ofi normal springs 144 and 145, and interrupter contact of the rotary magnet 107 to the back contact of armature 140, Where the circuit divides, one branch extending through the switching relay 100 to the grounded release trunk conductor 81, and the other branch extending by way of said armature 140, test wiper 131, test contact 140, and the Winding of relay 140 to ground. Resistance- 143 is relatively high and the ampere turns of the various relays involved are so. proportioned that relays 100 and 104 are not energized. Relay 146, however, is operated an d actuates the meter M and also lights the lamp L at the observing operators position. It is noted that relay 146 will be energized, as explained, upon the stopping of the first switch upon the eleventh contact in the first level, and the arrival of other switches at this contact will produce no effect on. relay 146 except to slightly increase the current flow through it.

Continuing with the consideration of the selector E, the rotary off normal springs 110, 111, and 112 are shifted at. the same time that the springs 108 and 109 are separated, that is, on the eleventh rotary step of the switch, and the lower side of the trunk line is therefore connected with the common conductor 113 extending to the observing operators position. Relay 141 is, therefore, energized over the calling line and lights the lamp L connected with the common conductor 113 in the same manner. The observing operator can now talk to the subscriber, or subscribers, as the case may be by operating the key K the same as was described in connection with the first selector D, and the key K and may advise them to hang up their receivers and (-all the desired number again after a shorttime, when it may be expected that trunk lines in the desired group will be available. lVhen one of the subscribers, the subscriber using the selector E for example, hangs uphis receiver the slow acting relay 103 is energized momentarily and grounds the test wiper 131,

thus short circuiting relay 146 and causing it to decnergize. Lamp L" is thus extinguished for an instant, and the meter magnet is deenergi'zed. As soon asthc slow acting relay 102 of the selector E falls back it restores the switch. to normal, ground is removed from the test wiper 131 and relay 146 being no longer short circuited will again energize by current through the stepping relays of the other selectors whichare standing on the eleventh contact in the first level. Thus the meter M is again operated. The same thing occurs as each of the other. switches is released, and the meter M is re-opcrated each time until the last switch.

is restored to normal. 'When this occurs since there are no switches remaining on the eleventh contact, the meter cannot again be operated and the registration in the case of the last switch is thus omitted, although it will be clear that the total number of registrations will be equal to the total number of switches which have stopped on the eleventh contact. Stated in another way, the meter is actuated once when the first switch stops on the eleventh contact and is actuated again whenever any switch, except the last, is released.

It has been assumed in the foregoing that the observing operator will come in and answer subscribers, whose lines have been extended to her position due to the lack of idle trunks. If desired, however. a permanent signal may be given such subscribers which will indicate to them automatically that the required number will have to be called over again. For this purpose the conductors 85 and 86 may be connected with. a lead coming from some well known form of busy signalling machine, so that the calling subscriber will be automatically given the busy signal in. case all the trunks in a' selected group are busy. The connection to the busy signalling machine may be permanent or keys may be provided by means of which the operator can efi'ect the connection at her discretion when she expects to be busy with other matters or intends to leave the switchboard.

Having described my invention, what I consider to be new and desire to have protected'by Letters Patent will be pointed out in the appended claims. i

What I claim as my invention is:

1. In an automatic telephone system, a group of subscribers lines, individual line switches for estending said lines when call-- ing, another line switch adapted to be substituted for the line switch normally assigned to a complainin subscribers line, talking conductors exten ing from said other line switch to an operators position, and signals at the operators position for indicating when the complaining subscriber is calling or being called.

2. In an automatic telephone system, a group of subscribers lines, individual line switches for extending said lines when calling, another line switch adapted to be substituted for the line switch normally assigned to a complaining subscribers line, talking conductors extending from said other line switch to an operators position, signals at the operators position for indicating when the complaining subscriber is calling or being called, and a key at the operators position for connecting the operators head set with said talking conductors, whereby the operator is enabled to listen in on outgoing or incoming connections.

3. In an automatic telephone system, a group of subscribers lines, a line switch, circuit arrangements whereby said line switch can be assigned at will to any line in said group, operators equipment associated with said line switch for supervising incoming and outgoing calls, and metering apparatus associated with said line switch for counting the total number of incoming and outgoing calls.

4. In an automatic telephone system, a plurality of groups of trunk lines, an automatic selector switch controllable over a calling subscribers line to select a desired one of said groups, means operated automatically for causing said selector to select an idle trunk line in the selected group, a single talking conductor extending from said switch to an operators position, contacts in said switch for connecting one conductor of the calling line to said talking conductor in case all of the trunk lines in the selected group are busy, means for signalling the operator, and means whereby the operator can establish a talking circuit over the said conductor to answer the calling subscriber.

5. In an automatic telephone system, a plurality of groups of trunk lines, an automatic selector switch controllable over a calling subscribers line to select a desired one of said groups, means operated automatically for causing said selector to select an idle trunk line in the selected group, a meter, circuit connections for operatin said meter in case the said selector findsal the trunk lines in the selected group busy, and means responsive to the release of said selector for closing said circuit connections.

6. In an automatic telephone system, a plurality of groups of trunk lines, an auto matic selector switch controllable over a callin subscribers line to select a desired one of said groups, means operated automatically for causing said selector to select an idle trunk line in the selected group, a meter, and circuit connections for operating said meter when the calling subscriber hangs up his receiver in case all of the trunk lines in the selected group are busy.

7. In an automatlc telephone system, a

. ity of selector switches for extending calling subscribers lines to idle trunk lines in selected groups, and a meter common to said groups and to said switches for registering the number of periods of time during which one or more calls are lost because no idle trunk lines in some group or groups are available.

8. In an automatic telephone system, a

plurality of groups of trunk lines, a plurality of selector switches for extending calling subscribers lines to idle trunk lines in selected groups, a meter common to said switches for registerin the number of periods of time during w ich calls are lost because no idle trunks are available, and individual meters for the trunk groups for indicating which of the groups contain an insufficient number of trunks.

9. In an automatic telephone system, a plurality of groups of trunk lines, a plurality of selector switches for extending calling subscribers lines to idle trunk lines in 'selected groups, a meter for each group of trunk lines, and circuit arrangements effective when a plurality of subscribers attempt to call while all the trunk lines in a selected group are busy for operating the meter associated with such group when one of the latter calling subscribers hangs up his receiver.

10. In an automatic telephone system, a plurality of selector switches, multiply connected bank contacts in said switches constituting terminals of trunk lines, another multiple bank contact ineach switch, a meter associated with said other bank contacts, means for causing any selector in use tostop on the meter bank contact in case all the trunk contacts are busy, and means for operating the said meter each time a selector which has stopped on the meter contact is released while there is one or more selectors positioned on multiples of said meter contacts.

11. In an automatic telephone system, a plurality of selector switches, multiply con nected bank contacts in said switches constituting terminals of trunk lines, another multiple bank contact in each switch, a meter associated with said other bank contacts, means for causing any selector in use to stop on the meter bank contact in case all the trunk contacts are busy, circuit connections such that the meter is operated the first time a selector stops on the meter bank contact, whereas if other switches stop on said bank contact before the first selector is released the meter will not be operated, and circuit connections for operating the meter each time a selector which has stopped on the J meter bank contact is released, except that when the last selector is released the meter is not operated.

12. In an automatic telephone system, a group of subscribers lines, individual line switches for extending said lines when calling, male and female jacks by means of which each line switch is normally connected to its associated line, a special line switch having its banks multipled with the other line switches and provided with a cable terminating in a male jack which may be substituted for the male ack of any individual switch, whereby the said special'line switch can be temporarily associated with a com plaining subscribers line in place of its individual switch, talking conductors extending from said special line switch to an operators position, and signals at the operators position for indicating when the complaining subscriber is calling or being called.

13. In an automatic telephone system, a group of subscribers lines, individual line switches for extending said lines when calling,'male and female jacks by means of which each line switch is normally connected to its associated line, a special line switch having its banks multipled with the other line switches and provided with a cable terminating in a male jack which may be substituted for. the male jack of any individual switch, whereby the said special line switch can be temporarily associated with any line 5 in place of its individual switch, and metering apparatus associated with said special line switch for counting the total number of incoming and outgoing calls.

14. In a telephone system, calling lines, a 100 group of trunk lines accessible to said-calling lines, selector switches for connecting said calling lines to idle trunks of said group, a meter for registering the number of calls which are lost due to all trunks, of 105 the group being in use, and circuit arrangements for operating said meter rendered effective either before or after a calling subscriber attempting to complete a call via said group has replaced his receiver on the switchhook.

15. In a telephone system, calling lines, a group of trunk lines accessible to said callin lines, selector switches for connecting said calling lines to idle trunks of said group, a meter for registering the number of calls which are lost due to all trunks of the group being in use, and circuit arrangements for operating said meter rendered eifective in certain cases after a calling subscriber attempting to complete a call via said group has replacied his receiver on the switchhook.

16.- In an automatic telephone system, a selector switch, groups of trunk lines accessible tosaid switch, a plurality of meters, there being one for each group of trunk lines, said meters accessible to said switch only when the trunks of their corresponding group are all in use, circuits for operating said meters includin relays of said selector switch, means in sai switch effective to prevent the operation of said relays when the meter is operated, and means for completing the meter operating circuit! 17. In an automatic telephone system, a plurality of selector switches, multiply connected bank contacts in said switches-constituting terminals of trunk lines, another multiply connected bank contact in each of said switches, a meter associated with said other bank contacts, means for causing any selector in use to stop on the meter bank contact in case all the trunk contacts are busy, acircuit for said meter, means for closing said circuit the first time a switch stops on a meter bank contact, and circuit connections for operating the meter each time a selector which stopped on the meter bank contact is released roviding' some other selector is still positioned on the multiple of said meter contact.

18. In an automatic telephone system, a

pluralit of selector switches, multiply connected ank contacts in said switches constituting terminals of trunk lines, another multiple bank contact in each switch, a meter associated with said other bank contacts, means for causing any selectors in use to stop on the meter bank contact in case all the trunk contacts are busy, a circuit for said meter,, means for causing any selector stopping on its meter contact to complete sald circuit, means operative responsive to a selector enga g its metering contact, while a multiple 0 the same is en aged by some other selector, for momentari y short circuiting said meter to effect its restoration and re-- operation, and means for causing only its restoration when the selector released is the last switch to disconnect from its meter contact.

In witness whereof. I hereuntosubscribe my name this 17th day of March, A. D. 1921.

CLARENCE E. LOMAX. 

